The present invention relates to a downhole tool for circulating fluid in a well bore and in particular, though not exclusively, to a circulation tool which can be selectively locked in an opened or closed configuration while in tension or compression.
At various times during the drilling, completion and production of an oil or gas well, it may be necessary to circulate fluid within the well bore. This is typically done by running a tool on a workstring, the tool having a cylindrical body with radial ports, through which fluid from the bore of the workstring can pass. The procedure can provide a cleaning action and/or provide a transport system to carry debris and other materials from the well bore to the surface in the circulating fluid.
A known circulating tool is that disclosed in GB 2272923. This tool for circulating fluid in a well bore comprises a body member having a radial fluid outlet. An isolation sleeve is movably mounted on the body member for movement between an open position in which fluid may flow out of the outlet and a closed position. The isolation sleeve is moved to its open position against the action of spring by engaging a shoulder with the top of a liner and setting down on the tubing string. Alternatively, the outlet is opened when the lower end of the tubing string engages the bottom of the well bore.
This tool has a number of disadvantages. The tool can operate only by contacting a formation in the well bore e.g. a liner top or bottom of the well, and thus cannot be operated at any desired location in the well bore. In contacting a formation the tool is held in compression which limits other functions which can be performed from the work string when fluid is circulated through the tool. Further any spurious debris in the well bore, or indeed sudden pressure changes within the well bore can cause the tool to operate prematurely.
U.S. Pat. No. 6,152,228 provides a circulation tool which overcomes the problem of premature operation. The tool comprises a tubular assembly which has an axial through passage between a fluid inlet and first fluid outlet. The fluid inlet and the first fluid outlet are connected in a work string which is supported from the surface above the well bore. There is a second outlet which extends generally transversely of the assembly. An obturating member is moveable between a first position in which the second fluid outlet is closed and a second position which permits fluid flow through the second outlet. An engagement mechanism is moveable between an engaged configuration in which the obturating member is maintained in one of the first and second positions, and a disengaged configuration in which the obturating member is in the other of the first and second positions. The tubular assembly is coupled to a shoulder which is engageable with the formation in the well bore to engage or disengage the engagement mechanism. Setting down weight on the work string causes a formation of the well bore to exert a force on the shoulder which results in the second outlet being opened.
As the engagement mechanism allow the tool to be maintained in either the open or closed configuration, the tool cannot be prematurely set. However, the major disadvantage of this tool is that its use is limited to locations within the well bore where a formation exists so that the tool must be placed in compression to switch configuration.
It is an object of the present invention to provide a circulation tool which can be selectively opened and closed without the need to set down weight on the tool or contact a formation in the well bore.
It is a further object of at least one embodiment of the present invention to provide a circulation tool which can be locked in an open or closed configuration to operate the tool in tension or compression.
It is a still further object of at least one embodiment of the present invention to provide a method of operating a circulation tool by varying fluid pressure through the tool from pumps located above the tool.